foo.cc: In function 'int main()':
foo.cc:10:27: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
      if(a%400==0||a%100!=0&&a%4==0)  cout<<"29"<<endl;
                   ~~~~~~~~^~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。